Method and apparatus for providing protected multilateral junctions

ABSTRACT

A method of providing a protected lateral well junction is disclosed. A milling assembly and whipstock are run into a cased primary wellbore to a desired depth and orientation. An anchor and packer are set. A window is milled in the cased borehole and a lateral rat hole is drilled. The milling assembly is removed, and the window and rat hole are filled with a protecting material, thereby covering any rough or jagged edges of the window. A new hole is drilled in the protecting material, through the window and into the lateral rathole, slightly offset from the window edges that are isolated by the remaining protecting material.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Provisional Application Serial No. 60/381,135 filed on May 16, 2002 in the name of Praful Desai as inventor.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] The present invention relates generally to a method and apparatus for the completion of multilateral wells, that is, when one or more lateral wells are drilled from a primary well bore. More particularly, this invention relates to a new and improved method and apparatus for providing a protected junction between the primary well bore and a lateral well bore.

[0005] 2. Background of the Invention

[0006] A multilateral well is typically drilled and extended from a primary or main well bore. The primary well bore can be vertical, angled, or horizontal. Multilateral technology can be applied to both new and existing wells, and provides operators several benefits and economic advantages over drilling entirely new wells from the surface. For example, it has become a common practice to drill deviated, and sometimes horizontal, lateral boreholes from a primary wellbore in order to increase production from a well. In addition to production cost savings, development costs also decrease through the use of existing infrastructure, such as surface equipment and the well bore. Multilateral technology expands platform capabilities where space is limited, and allows more well bores to be added to produce a reservoir without requiring additional drilling and production space on the platform. In addition, by sidetracking damaged formations or completions, the life of existing wells can be extended. Finally, multilateral completions accommodate more wells with fewer footprints, making them ideal for environmentally sensitive or challenging areas.

[0007] In a typical operation to drill a lateral borehole, a whipstock and mill assembly is used to create a window in the wall of the casing of the primary well bore. The whipstock is set on the bottom of the existing borehole or anchored within the borehole. The whipstock has a ramped surface that is set in a predetermined position to guide a mill in a deviated manner so as to mill away a portion of the wellbore casing, thus forming a window in the steel casing of the borehole.

[0008] The typical whipstock has a ramp or sloped surface whereupon the mill tool is urged outwardly until it is fully outside the casing. As the mill moves downward within the borehole, the ramped surface of the whipstock urges the mill radially outward so that the cutting surface of the mill engages the inner surface of the casing. As this engagement begins, the casing is cut away, thus beginning the upper end of the window. The ramp of the whipstock then causes further deviation of the mill, causing the mill to move downwardly and radially outward through the casing. In such a manner a longitudinal window is cut through the casing. Ultimately, the whipstock's ramped surface urges the mill radially outward to the extent that it is located entirely outside of the wellbore casing. Once this occurs, the mill ceases cutting the window. The lateral wellbore is then drilled through this window out into the formation where new or additional production can be obtained.

[0009] Traditional cutting techniques result in an upside-down “teardrop” shaped window. The teardrop shape of the window, however, can impede the ability to drill and complete the deviated borehole. Specifically, as the window narrows, the metal portion of the casing interferes with the ability to drill, place liner, screens and so forth.

[0010] Another problem associated with primary and lateral junctions is that the milling of the window through the primary wellbore casing usually results in jagged and rough window edges. After a lateral borehole is cut, it is common in the prior art to run a tubular device, such as a liner, into the lateral borehole. The jagged or rough edges of the casing window can damage the liner (especially expandable liners) and other well tools, such as screens, inflatables, elastomeric tools, and the like as they pass through the window in subsequent lateral operations. Further, it is particularly difficult to seal around the window that is of a peculiar shape and has a jagged edge around its periphery. There continues to be a need for new and improved methods and devices for providing such multilateral operations, and, particularly, operations where the intersection of the primary and lateral wells forms a smooth junction so as not to damage other well tools and parts as they go into and/or are retrieved from the lateral wellbore. The present invention relates to a new and improved method and apparatus for the construction of a protected multilateral well junction, and overcomes the deficiencies of the prior art.

BRIEF SUMMARY OF THE INVENTION

[0011] The present invention is direct to a protected junction at the intersection of a primary borehole and a lateral borehole comprising a primary casing having a window opening into the lateral borehole wherein the window edges are substantially covered by cement or gel.

[0012] The present invention is also directed to a method of providing a protected multilateral well junction. A milling assembly and whipstock are run into the primary well bore to a desired depth and orientated. An anchor and packer are set. A window is milled in the cased borehole and a lateral rat hole is drilled. The window has a longitudinal length and width. In the preferred embodiment, the window has a predetermined width and length that is slightly larger than full gage of the lateral borehole. The milling assembly is then removed, and the window and rathole are filled with a protecting material such as cement or gel, thereby isolating any rough or jagged edges of the window. The rough and jagged edges are thus coated with or covered by the protecting material. This way the rough and jagged edges become less prone to damaging tools going into or out of the window. A new, full-gage hole is drilled through the cement or gel material and into the lateral rathole, resulting in a smooth, full-gage hole, offset from the now covered jagged window edges.

[0013] Other objects and advantages of the invention will appear from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which:

[0015]FIG. 1 is a cross-sectional depiction of the milling operation.

[0016]FIG. 2 is a cross-sectional depiction of a multilateral junction after the milling assembly has been retrieved.

[0017]FIG. 3 is a cross-sectional view of a multilateral junction filled with a protecting material.

[0018]FIG. 4 is a cross-sectional view of the multilateral junction wherein the lateral drilling assembly is drilling through the protecting material and into the formation.

[0019]FIG. 5 is a cross-sectional view of the protected multilateral junction wherein the window edges are isolated by the protecting material.

NOTATION AND NOMENCLATURE

[0020] Certain terms are used throughout the following description and claims to refer to particular system components. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to. . . ”.

[0021] The present invention is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present invention with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein.

[0022] In particular, various embodiments of the present invention provide a number of different constructions and methods of operation. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results. Reference to up or down will be made for purposes of description with “up” or “upper” meaning toward the surface of the well and “down” or “lower” meaning toward the bottom of the primary wellbore or lateral borehole.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Referring now to FIGS. 1-5, there are shown the sequential steps of a preferred method of providing the protected junction of the present invention. Referring to FIG. 1, a milling assembly is lowered into a cased primary borehole 4 on a work string 3. The milling assembly may include a reentry tool, a spline sub, a retrievable anchor (not shown), a debris barrier or plug 5, a packer, a whipstock 10 having a ramp 12, and one or more mills 21 releasably attached at to the upper end of whipstock 10. The mills 21 are disposed on the end of the work string 3 extending to the surface. In a preferred embodiment, the milling assembly is lowered onto a well reference member (not shown) which has preferably previously been permanently installed at a predetermined location in the cased primary borehole for subsequent well operations. The well reference member may be termed an insert locator device (ILD) which replaces the typical big bore packer. A well reference member is shown and described in pending U.S. PCT Application Serial No. PCT/US01/16442 filed May 18, 2001 hereby incorporated herein by reference.

[0024] The ramp 12 of the whipstock 10 is oriented in the preferred direction of the window 60 to be cut in the casing 2. After the whipstock 10 is set, the work string 3 is rotated causing the mill 21 to shear a connection at the upper end of the whipstock 10. The mills 21 are then guided by the whipstock ramp 12 into the casing 2 as the work string 3 rotates the mills 21, causing them to cut a window 60 in the casing 2.

[0025] Referring now to FIG. 1, the mills 21 are shown cutting through the primary bore casing 2 to form a window 60. In the preferred embodiment, the resulting window 60 has a predetermined width that is slightly wider than the full gage desired in the lateral borehole. The window 60 is cut using conventional milling techniques. In the preferred embodiment of this invention, the window 60 is cut using techniques and apparatus described in U.S. Pat. No. 6,499,538 filed Apr. 8, 1999, entitled “Method and Apparatus for Forming an Optimized Window,” hereby incorporated herein by reference.

[0026] The use and configuration of these components in milling operations is well known by those skilled in the art. The work string is 3 rotated, thereby rotating the mills 21 as they move downwardly and outwardly on the ramp 12 of the whipstock 10. The ramp 12 guides the rotating mills 21 into engagement with the casing 2, thus cutting a window 60 in the casing 2. After cutting a window 60, the mills 21 continue to cut a rat hole 40 into the formation 100, as the beginning of the lateral borehole 41, best shown in FIG. 2.

[0027] Referring now to FIG. 2, once the rathole 40 has been cut, the work string 3 and mills 21 are retrieved and removed from the cased primary borehole 4. In an alternative embodiment, the whipstock 10 is also retrieved and replaced with a drilling deflector (not shown).

[0028] Using conventional materials and techniques, a protecting material 50, such as cement, gel or a like material is pumped down through the cased primary borehole 4, through the window 60 and into the lateral rathole 40, thereby filling the window 60, as shown in FIG. 3. Protecting materials may comprise conventional cement, polymer or monomer gels or like substance. For example, a polymer gel such as the Pro-Poxy 300 or Pro-Poxy 400 gel manufactured by Unitex may be used as a protecting material 50.

[0029] Referring now to FIG. 4, after the protecting material 50 has set, a smooth junction between the cased primary borehole 4 and lateral borehole 41 is formed by cutting out a portion of the protecting material 50. A drill string assembly 25 comprising a drill bit 26, mill, reamer or like cutting tool is run into primary borehole 4, cutting out the protecting material 50 in the primary borehole 4. As the drilling assembly 25 engages the ramp 12 of the whipstock 10, the assembly 25 is guided through the window 60 and into the lateral rat hole 40, continuing to cut out a portion of the protecting material 50. In the preferred embodiment of this invention, the drilling assembly 25 drills a hole with a diameter of full gage or less through the protecting material 50. As the drilling assembly 25 passes through the window 60, any jagged or rough edges of the window are, thereby, isolated by the remaining protecting material 50. As best shown in FIG. 5, any jagged or rough edges of the window 60 are isolated, thus eliminating potential damage to tubulars or sealing devices subsequently passing through the window 60. Having provided a smooth junction between a primary 4 and lateral borehole 41, screens, liners, expandable tubulars, sealing tools or the like may be run through protected junction and into the lateral bore 41.

[0030] In an alternative embodiment, after completing the full gage lateral bore hole through the protecting material, the drilling assembly continues drilling beyond the existing lateral rathole 40, and into the formation 100. Once the lateral borehole 41 has been drilled to the desired depth, the drill string is removed and retrieved to the surface.

[0031] In another alternative embodiment, upon completing the drilling of the lateral rathole 41, a whipstock retrieval tool may be lowered and connected to the upper end of whipstock 10. The plug 5 and/or retrievable anchor are released from the cased borehole 4 and the whipstock 10 and assembly is retrieved. After the whipstock 10 and assembly are removed from the primary wellbore 4, the area in the primary borehole below the window may be cleaned out by removing any remaining protecting material 50, or other obstructions, giving access to both the primary 4 and lateral 41 boreholes. If retrieval of the whipstock assembly is not possible by retrieval device, its removal may be accomplished by other methods known by those skilled in the art. Providing access to the primary wellbore below the window may or may not be used in the present invention and is an alternative embodiment.

[0032] The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications. 

What is claimed is:
 1. A method of forming a protected multilateral well junction at the intersection of a primary borehole having a casing and a lateral borehole, the method comprising: cutting a window in the casing of the primary borehole; filling said window with a protecting material; and drilling the lateral borehole through said window and said protecting material, whereby a portion of said protecting material remains in said window thereby isolating said casing from said lateral borehole.
 2. The method of claim 1, further comprising running a tubular into said lateral borehole.
 3. The method of claim 2, wherein said tubular is an expandable tubular.
 4. The method of claim 3, further comprising expanding said expandable tubular in said lateral borehole.
 5. The method of claim 1, further comprising running a screen into said lateral borehole.
 6. The method of claim 1, wherein said window has a predetermined width and the lateral borehole has a diameter that is less than said predetermined width.
 7. The method of claim 1, wherein said window has a longitudinal length and a substantially uniform width along the longitudinal length.
 8. A method of forming a protected multilateral well junction at the intersection of a primary borehole having a casing and a lateral borehole, the method comprising: lowering a milling assembly releasably connected to a whipstock and plug assembly into the primary borehole; anchoring the whipstock and plug assembly with the casing at a predetermined position and orientation; disconnecting the milling assembly from the whipstock and plug assembly; lowering and rotating the milling assembly having at least one cutting member; guiding the cutting member towards the casing along a ramp on the whipstock until a window is cut in the casing of the primary borehole; retrieving the milling assembly from the primary borehole; inserting a protecting material into the primary borehole and filling said window with said protecting material; lowering a drilling assembly into said primary borehole; removing said protecting material from the primary borehole; guiding the drilling assembly through the window and drilling the lateral borehole through said window and said protecting material, whereby a portion of said protecting material remains in said window thereby isolating said casing from said lateral borehole; and retrieving said drilling assembly from the primary borehole.
 9. The method of claim 8, further comprising running a tubular into said lateral borehole.
 10. The method of claim 9, wherein said tubular is an expandable tubular.
 11. The method of claim 10, further comprising expanding said expandable tubular in said lateral borehole.
 12. The method of claim 8, further comprising running a screen into said lateral borehole.
 13. The method of claim 8, further comprising retrieving said whipstock and plug assembly from the primary wellbore.
 14. The method of claim 8, wherein said window has a predetermined width and the lateral bore has a diameter that is less than said predetermined width.
 15. The method of claim 8, wherein said window has a longitudinal length and a substantially uniform width along the longitudinal length. 